22 percent of obese children had antibodies compared with 7 percent of normal-weight kids — but the obese kids with evidence of prior adenovirus-36 infections were on average about 35 pounds fatter than obese children who hadn’t caught the virus.

Thus, a cold virus could account for a significant share of all obesity and have a particularly great impact of extreme obsesity.

Chickens, mice, rats and monkeys infected with the virus all get fat even though the animals don’t eat more or exercise less than they did before they were infected. Experiments on human cells in laboratory dishes explain how the virus promotes weight gain — adult stem cells infected with the virus make more fat cells, and those fat cells store more fat. . . . About 30 percent of obese adults carry antibodies against adenovirus-36 while about 10 percent of normal-weight people do[.]